Polymer products and multi-stage polymerization processes for the production thereof
Multi-stage polymerization processes that produce polymers having controlled compositions and molecular weight with improved catalyst productivity are disclosed. An example method for producing a multi-modal polyolefin comprises polymerizing the multi-modal polyolefin in the presence of a metallocene catalyst system in at least a slurry-phase polymerization stage and a gas-phase polymerization stage arranged in series in any order, wherein the multi-modal olefin comprises: (i) a first polyolefin fraction having a density of less than about 940 kg/m 3 , and (ii) a second polyolefin fraction having a density of less than about 930 kg/m 3 .
1. A process for producing a multi-modal polyolefin, comprising:
polymerizing the multi-modal polyolefin in the presence of a metallocene catalyst system in at least a slurry-phase polymerization stage and a gas-phase polymerization stage arranged in series in any order, wherein the multi-modal polyolefin has a molecular weight distribution (Mw/Mn) of greater than 2 to about 10 and comprises: (i) a first polyolefin fraction having a density of less than about 940 kg/m 3 , and (ii) a second polyolefin fraction having a density of less than about 930 kg/m 3 and wherein the metallocene catalyst system comprises (C 5 H 3 Me,n-Bu) 2 ZrCl 2 , where Me is methyl Bu is n-butyl.
2. The process of claim 1 wherein the first polyolefin fraction has a density of less than about 930 kg/m 3 .
3. The process according to claim 1 wherein the second polyolefin fraction has a density of less than about 925 kg/m 3 .
4. The process according to claim 1 wherein the first polyolefin fraction has a melt index of 1 dg/min or greater, and wherein the second polyolefin fraction as a melt index of 3 dg/min or less.
5. The process according to claim 1 wherein the first polyolefin fraction has a melt index of 5 dg/min or greater.
6. The process according to claim 1 wherein the second polyolefin fraction as a melt index of 1 dg/min or less.
7. The process according to claim 1 wherein first polyolefin fraction is present from about 30% to about 50% by weight of the multi-modal polyolefin, and wherein the second polyolefin fraction is present from about 70% to about 50% by weight of the multi-modal polyolefin.
8. The process according to claim 1 wherein ethylene is present in the slurry-phase polymerization stage in an amount ranging from about 3 mol % to about 10 mol %, and wherein a co-monomer is present in the slurry-phase polymerization stage in an amount ranging from about 0.05 to about 0.6 mole of the co-monomer per mole of the ethylene.
9. The process according to claim 1 wherein the gas-phase polymerization stage has an ethylene partial pressure of about 6 bar to about 25 bar and wherein a co-monomer is present in the gas-phase polymerization stage in an amount ranging from about 0.03 to about 0.08 mole of the co-monomer per mole of the ethylene in the gas phase.
10. The process according to claim 1 wherein the multi-modal polyolefin comprises polyethylene.
11. The process according to claim 1 wherein at least ethylene and a co-monomer are polymerized to produce the multi-modal polyolefin.
12. The process according to claim 11 wherein the co-monomer used in the slurry reactor is 1-butene and the co-monomer used in the gas phase reactor is 1-hexene.
13. The process according to claim 11 wherein the co-monomer comprises from 3 to 12 carbon atoms.
14. The process according to claim 1 wherein the slurry-phase polymerization stage precedes the gas-phase polymerization stage.
15. The process according to claim 1 wherein the slurry-phase polymerization stage comprises a loop reactor.
16. The process according to claim 1 wherein hydrogen gas is introduced into slurry-phase polymerization stage and into the gas-phase polymerization stage.